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This paper describes the substantial potential of tidal barrage solutions for renewable energy generation in the UK. It demonstrates that installations on as few as eight major estuaries should be capable of meeting at least 10% of present electricity demand, and possibly significantly more, employing fully proven technology. This should be achievable, under favourable UK Treasury discount rates, at unit electricity prices that are likely to be competitive against future costs of alternative sources. This potential substantially exceeds that of 'tidal stream' turbine or practicable 'lagoon' systems, much vaunted in recent times. It also draws attention to a recent study investigating the tidal power potential in the north-west of England.
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Proceedings of the Institution of
Civil Engineers
Maritime Engineering 162
December 2009 Issue MA4
Pages 155–164
doi: 10.1680/maen.2009.162 .4.155
Paper 900007
Received 25/02/2009
Accepted 17/03/2009
Keywords:
dams, barrages & reservoirs/
hydraulics & hydrodynamics/
renewable energy
Richard Burrows
Nicolas C. Yates
Terence S. Hedges
Ming Li
Jian G. Zhou
Daoyi Y. Chen
Department of
Engineering, University
of Liverpool, UK
Ian A. Walkington
Judith Wolf
Jason Holt
Roger Proctor
Proudman
Oceanographic
Laboratory,
Liverpool, UK
Tidal energy potential in UK waters
R. Burrows BEng, PhD, CEng, FICE, MCIWEM, I. A. Walkington BSc, PhD, N. C. Yates BSc, T. S. Hedges Eur Ing,
MEng, CEng, MICE, FRMetS
,M.LiMSc, PhD, J. G. Zhou MSc, PhD, D. Y. Chen BEng, MPhil, PhD, J. Wolf BSc, PhD, J. Holt
BSc, PhD and R. Proctor BSc, PhD
This paper describes the substantial potential of tidal
barrage solutions for renewable energy generation in the
UK. It demonstrates that installations on as few as eight
major estuaries should be capable of meeting at least 10% of
present electricity demand, and possibly significantly more,
employing fully proven technology. This should be achiev-
able, under favourable UK Treasury discount rates, at unit
electricity prices that are likely to be competitive against
future costs of alternative sources. This potential substan-
tially exceeds that of ‘tidal stream’ turbine or practicable
‘lagoon’ systems, much vaunted in recent times. It also
draws attention to a recent study investigating the tidal
power potential in the north-west of England.
1. INTRODUCTION: OFFSHORE RENEWABLE
ENERGY POTENTIAL IN UK WATERS
The medium- to long-term procurement of energy and the
related issue of climate change are set to remain at the top of
government and public agendas, both nationally and inter-
nationally, for some time to come. No clear vision has yet
emerged for a sustainable global energy future; and the
combination of rapid growth in both economies and populations
in the developing world are set to place extreme pressure on
fossil fuel reserves. It seems inevitable, therefore, that as the
twenty-first century evolves, ever-greater utilisation must be
made of renewable energy resources if the means for modern
living are to be preserved. From the perspective of the global
community, it is argued that it will ultimately become an
obligation for all societies to properly and fully exploit, for the
common good, the renewable energy resources at their disposal.
The geographical location of the United Kingdom and the seas
that surround it provide internationally enviable renewable
resources. Technologies for wind power extraction are now
mature and an increasing role for the opportunistic capture of
this intermittent energy source for the electricity grid is firmly
established. Marine wave energy offers even greater scope for
the future with a somewhat lower degree of unpredictability but
the necessary technological advances are still outstanding at
present. Even more exclusive, however, is the potential for tidal
energy extraction from around the UK coastline. The most
attractive locations for harnessing tidal power are estuaries with
a high tidal range for barrages, and other areas with large tidal
currents (e.g. straits and headlands) for free-standing tidal
stream turbines. Pertinent here is the fact that tidal barrage
solutions, drawing on established low-head hydropower tech-
nology, are fully proven. The La Rance scheme in France has
now passed 40 years of operation.
1–3
Of about 500–1000 TWh/year of tidal energy potentially available
worldwide,
4
the UK is estimated
5
to hold 50 TWh/year, repre-
senting 48% of the European resource, and few sites worldwide are
as close to electricity users and the transmission grid as those in
the UK. Following from a series of studies for the Department of
Energy (DoEn) in the 1980s,
6–9
16 estuaries were identified where
tidal barrages should be capable of procuring over 44 TWh/year.
In fact the bulk of this energy yield would accrue from eight major
estuaries,
4,9
in rank order of scale, the Severn, Solway Firth,
Morecambe Bay, Wash, Humber, Thames, Mersey and Dee. The
recent Sustainable Development Commission (SDC) report,
10
having revitalised interest in tidal energy, focused on the Severn
Estuary and unfortunately overlooked the full potential of UK
estuaries. A more recent review by Fells Associates
11
further
promotes the reappraisal of tidal barrage solutions, arguing that
previously held concerns over environmental impact require
urgent reassessment in the light of present climate change and
energy sustainability challenges, thus being supportive of the
Government’s ongoing 2-year strategic environmental assessment
for tidal energy from the Severn.
12,13
2. ENERGY FROM TIDAL BARRIERS AND
TIDAL STREAMS
The earlier estimates of UK tidal barrage potential amounted to
approximately 20% of UK electricity need in the late 1980s but,
following increases in electricity consumption, dropped to 15% (as
suggested by the Department of Trade and Industry in 2005). This
tidal energy extraction has the added benefit over wind- and wave-
based renewable resources of being fully predictable. In addition to
barrage solutions to tidal energy capture, there is also more modest
scope for tidal stream energy generation using submerged rotors,
either free-standing or as part of a ‘tidal fence’, these extracting
from the kinetic energy of the tidal flows. The SDC report
10
offers
figures for the potential from tidal streams amounting to about 5%
of electricity demand. With attention inevitably to be placed upon
reduced energy consumption and demand management, a future
tidal power contribution in excess of 20% of UK electricity demand
would, therefore, appear realistic.
Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al. 155
Although all tidal energy generation would be intermittent
locally, covering 8–11 h per day, normally in two pulses for ebb
phase operation, synchronised with the approximately 12?5h
tidal cycle, tidal phase lag around the coastline provides an
opportunity for the grid input window to be extended. With its
complete predictability, and operating in a mix with thermal,
hydropower and nuclear production as well as thermal renew-
ables, an effective base-load role should be attainable.
The case for a tidal barrage in the Severn estuary, with the
highest tidal range in Europe, is being actively promoted by the
Severn Tidal Power Group with increasing influential sup-
port.
10–13
This scheme alone (the smaller ‘inner’ of two earlier
options
4,9
) would be capable of meeting about 5% of current UK
electricity need.
14
The estuaries of the north-west of England offer fully
complementary potential to the Severn by virtue of the tidal
phase lag, as will be illustrated in Section 4. The Dee, Mersey,
Ribble and Wyre estuaries, Morecambe Bay and the Solway Firth
all have a macro-tidal range. Based on the earlier studies,
4,6,7,9
a total installed capacity of 12 GW was estimated (Ribble
excluded), with a potential energy yield of at least
17?5 TWh/year, which is approximately 5% of UK national need
and by inference a sizeable proportion (about half) of the
electricity demand of the north-west. Of all potential UK sites,
the Mersey with a very narrow mouth and, therefore, needing a
relatively short barrage length,
7,15
could offer power production
at the lowest unit cost.
4,9
In this region of the eastern Irish Sea, exploitable tidal stream
resources have also been identified to the north-west of
Anglesey and to the north of the Isle of Man, with more localised
resources in the approaches to Morecambe Bay and the Solway
Firth.
16
However, in estuaries it is unlikely that tidal stream
options can come close to the energy yield of barrage
alternatives. Recent assessments for the Mersey
17
offer estimates
of 40–100 GWh for tidal stream arrays, contrasting with
1200 GWh estimated for a barrage at an equivalent location. In
a similar vein, whereas offshore tidal lagoons are often mooted
as a viable alternative to estuary barrages, offering a similar
operational function, it is highly unlikely that they could be
realised at a comparable scale and remain competitive on cost
against the major barrage schemes cited above, by virtue of the
larger containment perimeter.
A barrage solution attempts merely to delay the natural motion
of the tidal flux as sea level changes: holding back the release of
water as tide level subsides under ‘ebb generation’ so that ‘head’
(water level) difference is sufficient for turbine operation;
deferring the entry of rising tidal flow to the inner estuary basin
for ‘flood generation’; or ‘dual mode’, a combination of both.
Each mode has some restricting effect, so reducing the range of
tidal variation within the basin, with ebb generation solutions
uplifting mean water levels, flood generation reducing mean
levels and dual-mode operation resulting in little change, as
illustrated in Figure 1.
A degree of environmental modification is, therefore, inevitable,
but this does not necessarily imply serious degradation from a
physical or ecological perspective, although issues related to
protection of habitats inevitably need to be confronted. Barrage
schemes are unique among power installations, being inherently
multi-functional infrastructure, offering flood protection, pos-
sible road and rail crossings and significant amenity/leisure
opportunities, among other features. Thus, a fully holistic
treatment of overall cost–benefit is imperative for robust
decision-making. It is suggested that, to date, this position has
been inadequately addressed in the formulation of energy
strategy, especially in respect of the potential strategic roles of
barrages in flood defence and transportation planning. It
follows, therefore, that apart from the direct appraisal of energy
capture, other complementary investigations must be suffi-
ciently advanced to enable proper input in decision-making in
respect of these ‘secondary’ functions, as well as the various
potentially adverse issues, such as sediment regime change,
impact on navigation and environmental modification. It is
hoped that the ongoing study for the Severn will resolve the
impasse.
13
3. TAPPING THE TIDAL POWER POTENTIAL OF
THE EASTERN IRISH SEA
A recent research project (2006–2008), conducted jointly by the
University of Liverpool and Proudman Oceanographic
Laboratory for the Joule Centre (with financial support from the
North-West Development Agency) aimed to assess the tidal
power potential of the eastern Irish Sea.
18
A generic regional
modelling approach was adopted to study the interaction
between the practicable exploitation of tidal energy and
potential hydrological, morphological and environmental
impacts. Its principal study objective was to estimate the
realisable tidal energy potential of the coasts of the north-west
of England, stretching from the Dee estuary to the Solway, with
regard to the installation of estuary barrages, tidal fence
structures or tidal stream rotor arrays, or combinations thereof.
At the time of writing, the conjunctive multi-barrage scheme
energy outputs are under final validation testing, but an
overview of the energy estimation process is provided below
through illustrations from the investigations completed for the
Dee estuary. An accompanying paper in this volume by Wolf et
al.
19
discusses environmental issues arising from these potential
developments.
3.1. 0D modelling
A zero-dimensional (0D) (flat-estuary or two-tank) model has
been employed in the project to synthesise barrage operation,
with realistic turbine characteristics relating flow rate Q,
diameter D and head H to the efficiency g and power P,as
defined by the Hill-chart shown in Figure 2. Note that r is the
density of the water, g is the gravitational acceleration and g is
the efficiency of the turbine, values for g in the chart
representing percentages of the maximum efficiency. As such
maximum values can be commercially sensitive, a conservative
assumption has been taken by adopting best g 5 80% herein.
This form of assessment is consistent with that used in earlier
preliminary studies and has been formulated into the Matlab-
based routines, depicted in Figure 3, illustrating ebb generation
for a scheme of 40 turbines (8 m diameter 21 MW) on the Dee
estuary. The barrage alignment, proposed earlier,
6,7
is shown in
the main part of Figure 4. Note that, in the simulations, a slight
bias is evident in the first few cycles due to initiation error.
In the routines, energy capture can be maximised by choosing a
suitable ‘delay’ after the chosen minimum generation head is
156 Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al.
reached (these figures being 2?56 h and 1 m, respectively, in
Figure 3). The effect of holding the water level during the delay
period can be seen in Figure 1. The runs presented have been
based on an assumed minimum water depth at low water spring
tide of 13 m, less than the main channel depths, to provide
added flexibility in the location of the turbines. The routine
ensures that cavitation is avoided by controlling the chosen
speed of revolution of the turbines, this being especially critical
for these runs since the 8 m diameter turbine is 2 m larger than
that considered earlier.
6
Figure 1 illustrates the water level variation for the Dee scheme
and Figure 5 shows similar output, together with the corre-
sponding power pulses arising from this 40-turbine set-up under
both ebb and dual (two-way) generation over the full spring to
neap tide sequence. The ebb mode produces 1?35 TWh and dual
mode produces 1?30 TWh, assuming a relative turbine efficiency
under ‘reverse’ flood-phase generation of approximately 80%.
Note that the flood-only mode achieves only 0?79 TWh due to
the smaller volumes mobilised and the lower head difference
arising from the shelving estuary bathymetry.
Figure 5 also shows a simulation of a scheme with a much
higher installed capacity of 120 turbines operating in dual
mode. This scheme comes close to maintaining the tidal range in
the basin by effectively producing a lag in the tidal phase
through the structure and produces significantly more energy,
but in the form of shorter higher power pulses that may be
difficult to assimilate into the electricity grid. Figure 6 shows
the increased amount of annual energy generated against the
number of turbines for both ebb and dual mode operation, both
with and without positive (peak level) pumping to heads up to
1 m. For the dual mode runs, the number of 12 m 6 12 m
sluices has been reduced from 40 used in the ebb runs to 20, but
in both cases sluicing is assisted by free passage through turbine
ducts. In producing these outline results, a delivery flow rate
matching the turbine flow at 1 m head has been taken when
operating the turbines as pumps; and the pump efficiency is
assumed to be 40% in allowing for the energy cost of pumping.
Note, also, that Figure 6 considers turbine installations extend-
ing far beyond the limit of practical viability.
The relative scale of turbine installation adopted from the
Severn Tidal Group studies formed the basis of the DoEn
follow-up studies,
6,7
namely ebb mode being favoured with
turbine numbers roughly compatible with extracting about 50%
of the available ebb-phase energy. This results in tidal levels in
the estuary basins dropping only to mean sea level or
Ebb
4
3
2
1
0
_
1
_
2
_
3
_
4
64
.
5
Time: days
55
.
543
.
53
4
3
2
1
0
_
1
_
2
_
3
_
4
64
.
5
Time: days
55
.
543
.
53
4
3
2
1
0
_
1
_
2
_
3
_
4
64
.
5
Time: days
55
.
543
.
53
Dual
Flood
Water depth: m Water depth: m Water depth: m
Figure 1. Different operational modes for a Dee Barrage scheme with 40 turbines (8 m diameter, 21 MW) showing external tidal
elevation (solid line) and reduced basin level variations (dashed line) (mAOD) plotted against time (days)
Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al. 157
thereabouts, and in this respect is consistent with the theoretical
approach put forward by Prandle.
20
From hereon, schemes with
these characteristics are referred to as ‘16DoEn’ turbine
installations.
Figure 7 shows estimates of the unit cost of electricity produced
by a Dee scheme, based on the procedure developed in the 1980s
DoEn studies,
6,7
and updated using the figures presented for the
Severn by the SDC
10
assuming UK Treasury funding at a 3?5%
discount rate. It is seen that the ebb mode of operation with
moderate turbine capacity (40 turbines representing a ‘16DoEn’
installation), as proposed in all earlier UK studies,
6,7
achieves the
minimum unit cost. However, installing two to three times the
number of turbines (‘26DoEn’ and ‘36DoEn’ solutions) offers
the theoretical possibility of doubling the total energy capture,
and may still be competitive (at unit costs in the region of
10p/kWh seen for the Dee) against alternative energy sources,
especially so as fossil fuel prices rise in the future. It is to be
noted that the SDC report
10
shows figures close to 10p/kWh for
the unit cost of energy from offshore wind installations which
Specific discharge, Q
11
6
.
0
6
.
4
5
.
6
5
.
2
4
.
8
4
.
4
4
.
0
3
.
6
3
.
0
2
.
6
A
Max output
2
.
4
2
.
0
1
.
6
1
.
2
0
.
8
0
.
4
140 160 180 200 220 240 260 280 300 320 340
Unit speed, g
11
360 400380 420 440 460 480
_
20
_
15
_
10
_
5
10
5
0
23
33
45
55
66
77
79
81
86
88
91
.
7
93
.
5
96
98
99
99
.
5
max
=
15
g 0%
C
500 520
Specific
Q
11
=
Q/(D
2
H
0
.
5
)
P
=
rgQHg
n
11
=
n D/(H
0
.
5
)
Power
Unit speed
discharge
Note: g
=
g/best g
b
2
B
Figure 2 The Hill-Chart describing the performance characteristics of a double-regulated bulb turbine (after Baker
4
)
Figure 3. Screen image showing: top turbine performance characteristics; middle tidal and reduced basin level variations; and
bottom power outputs
158 Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al.
receive strong backing at present. It must be noted, however,
that these figures are theoretical estimates (from 0-D modelling)
and hydrodynamic considerations external to the barrage
(covered by two-dimensional modelling) might be expected to
constrain these energy extraction gains.
As a more speculative alternative to this Dee barrage alignment,
Figure 4 also shows an extended ‘Dee–Wirral lagoon’ scheme
which extends the barrage in front of the Wirral peninsula to
take advantage of the shallow Burbo Bank on the southern and
western sides of the shipping entrance to the Port of Liverpool.
This scheme, as well as enhancing flood protection to the Wirral
coast, would increase the Dee tidal prism by a factor of 3 and,
with 150 turbines (,16DoEn), could generate 4?6 TWh
annually under ebb mode operation at a unit cost less than 20%
greater than the basic Dee estuary scheme, and still within the
10p/kWh threshold. It would similarly have scope for further
energy capture if dual mode were combined with an enhanced
installed capacity. It is also interesting to note that applying
similar methods to an alternative circular tidal lagoon off the
coast with identical tidal prism and energy capture would work
out at least 40% more expensive in unit cost terms without the
flood protection and amenity benefits.
Liverpool
Bay
Liverpool
Wirral
Mersey
N
0 5 10 km
Dee
North Wales
N
0 5 10 km
Figure 4. A potential Dee barrage alignment and an extended
Dee–Wirral lagoon
Ebb 40×21 MW
turbines
Dual 40×21 MW
turbines
Dual 120×21 MW
turbines
Power: MW
Water depth: m
900
4
3
2
1
0
_
1
_
2
_
3
_
4
012345678
800
700
600
500
400
300
200
100
0
01234
Time: days
Time: days
Water depth: m
4
3
2
1
0
_
1
_
2
_
3
_
4
012345678
Time: days
Water depth: m
4
3
2
1
0
_
1
_
2
_
3
_
4
012345678
Time: days
5678
Power: MW
700
600
500
400
300
200
100
0
01234
Time: days
5678
Power: MW
2500
2000
1500
1000
500
0
01234
Time: days
5678
Power
Basin/tide levels
Figure 5. Power outputs and basin levels under a spring–neap tide sequence
Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al. 159
3.2. Two-dimensional modelling
All the above outputs arise from the 0D model which accounts
for the hydraulics of flow through the turbine but does not
account for the hydrodynamics either side of the barrage. It has
been estimated that minor losses associated with flow entrance
to and exit from the turbine ducts might reduce energy capture
by 3–12%. Of more concern might be the effect of the energy
extraction on the tidal range at the barrage or on the ability of
the water in the basin to travel along the estuary, residual
energy being needed to overcome bed friction. To this end, it is
necessary to consider the barrage and turbine operation in a
two-dimensional (2D) model. Such a model has been produced
in the present study using Adcirc, a US government-funded tidal
prediction model. An interim computational domain for the
finite-element unstructured grid model is depicted in Figure 8.
This has over half a million elements, providing a resolution in
the estuaries down to about 50 m.
Barrages with the same hydraulic characteristics as those used in
the 0D model have been inserted in the 2D model and a snapshot
of output for the Dee and Mersey is shown in Figure 9. This
illustrates flows passing through the turbines and sluices and the
detailed representation of wetting and drying achieved from the
light detection and ranging (Lidar)
19
bathymetry incorporated
for both the Dee and the adjacent Mersey estuary, with its
barrage functioning also. At the time of writing, final fully
validated outputs were not available but these will be
presented
18
at www.liv.ac.uk/engdept/tidalpower. However, it
has been observed that the channels and banks in the vicinity of
the Dee turbines, which are squeezed into the western channel,
appear to have a significant constraining effect on the head
differences across the structure, so diminishing the energy
capture predicted from the 0D modelling. This contrasts with the
behaviour observed for the relatively deeper Severn estuary
where the predictions from 2D show much better agreement
with the 0D outcomes, as found in the earlier 2D modelling by
Proctor.
21
The objectives of the 2D modelling, within the ongoing Joule
Centre-funded project, extend to evaluation of any impact on
the overall tidal dynamics of the Irish Sea as a consequence of
the energy extraction from the conjunctive operation of the
barrages discussed herein (those in the estuaries of the north-
west of England together with the Severn) as well as potential
sites for major tidal stream arrays. Implications, if any, from
biophysical coupling in the marine ecosystem, manifesting
water quality or ecological consequences, were also to be
reviewed
18
and Wolf et al.
19
(in this issue) provide some insight.
Companion studies on the impact of barrage operation on the
estuarial sediment regime are currently under way at Liverpool,
using a 2D Telemac model of the Dee and Mersey estuaries.
4. ENERGY GENERATION FROM EIGHT MAJOR
UK BARRAGES
To appraise the potential inputs into the UK electricity grid from
major barrage installations, simulations were conducted using
the 0-D model as a preliminary to the main investigations
outlined in Section 3. As far as possible, an attempt was made to
consider equivalent barrage power schemes to those adopted in
the earlier DoEn studies (i.e. similar number and size of turbines
and sluices and similar generator capacities), although limita-
tions in detail available in the literature led to the need for
assumptions and compromises in the technical details. Figure 10
illustrates potential outcomes from the introduction of the eight
major barrage schemes discussed earlier.
4,9
These show the
combined power outputs, from the favoured ebb generation
using double-regulated axial flow turbines at each of the
barrages, noting that the Matlab routines developed for the
present study under-predict the earlier DoEn findings by about
15%. It is immediately apparent that they form essentially two
distinct ‘co-phase’ focused groups, the Severn/Wash/Humber
and the Eastern Irish Sea complement comprising the Solway,
Morecambe Bay, Mersey and Dee, with the Thames lying
somewhere in between.
The operation strategy depicted in Figure 10 is that configured
to provide maximum energy from each barrage by suitable
choice of ‘delay’ before generation commences, after the
minimum generating head is reached, and without pumping.
The simulation was undertaken for 28 tides representing a
spring–neap–spring series, as shown in part (a), whereas (b) and
(c) show the power produced over 2-day periods from the neap
and spring phases, respectively.
The north-west group of estuary barrages would operate in a
complementary fashion to the Severn (and ‘phase-aligned’ Wash
3
2
.
5
1
.
5
1
0
.
5
20
40
60 80 100 120
Number of turbines
140 160
180
200
220
240
260
280
300
320
2
Annual energy generation: TWh
Dual pump
Ebb no pump
Ebb pump
Dual no pump
Figure 6. Annual energy (TWh) outputs from the Dee scheme
with increase in the number of turbines installed over a range
from 20 to 320
Unit cost of electricity: p/kWh
30
.
00
25
.
00
20
.
00
15
.
00
10
.
00
5
.
00
20 40 60 80 100 120 140 160 180200 220 240 260 280300 320
Number of turbines
Dual no pump
Ebb no pump
Ebb pump
Dual pump
Figure 7. Estimated unit cost (p/kW h) for Dee schemes with
different number of turbines
160 Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al.
and Humber). It should be noted that only approximate
estimates of tidal phase have been used herein, based mostly on
records from the nearest ports and so slight adjustments to the
synchronisation might be expected from a more refined
analysis. By judicious use of pumping to enhance water capture
around high tide (essentially short-term ‘pumped storage’) and
Figure 8. The 2D Adcirc model domain; left panel is the whole grid; upper right is the upper Irish Sea; and bottom right is a close-up of
the Dee and Mersey estuaries with barrages in place
Vector legend
4
.
55 m/s
0
.
00 m/s
0 00:30:00
Figure 9. Simulation of barrages operating in the Dee and Mersey estuaries from the Adcirc model, arrows showing instantaneous
current velocity vectors; a 36DoEn turbine installation with turbine banks on the main left (west bank) channel and in a secondary
channel towards the right, near the end of a generation cycle with levels near equalised
Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al. 161
optimal conjunctive operation of the individual schemes, and by
generating as soon as head differences permit, it would seem
possible that the smaller power gap between the Severn group
outputs and the following north-west group peaks might be
smoothed out to some degree. It appears less likely that such
action could eliminate the major daily trough, during which
only the Thames makes a significant contribution. Other
potential estuary barrage or lagoon locations, for example
Power output: GWPower output: GWPower output: GW
12
10
8
6
4
2
0
0 50 100 150 200 250 300 350
Time: h
(b)
(a)
10
12
8
6
4
2
0
160 165
170 175 180 185
Time: h
190 195 200 205 210
12
10
8
6
4
2
0
15 20 25 30 35 40 45 50 55 60
Time: h
(c)
Severn
Solway
Morecambe Bay
Wash
Mersey
Dee
Humber
Thames
Figure 10. (a) 28 tide spring–neap–spring series; (b) 2-day segment from neaps; (c) 2-day
segment from springs
162 Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al.
around the east coast of Scotland, may be worthy of future
consideration, or else different modes of operation may need to
be considered. Flood generation or dual mode operation,
although generally less cost efficient in energy conversion than
ebb generation, may provide the added flexibility necessary to
provide a significant 24 h output to the grid.
Whereas, therefore, the ability to offer a balanced daily supply
remains unproven at this point, it is clear that substantial
contributions to daily electricity demands could be made. From
the preliminary analysis presented earlier
22
employing no
generation delays for the widest generation windows for each
scheme, it appears that for much of the day, tidal power
contributions of close to 6 GW could be provided during
‘springs’, falling to around 2 GW during ‘neaps’. These figures
should be set against typical power demands in summer
ranging, approximately, from 25–40 GW and in winter from
30–50 GW.
The annual energy output from the ‘maximum energy’
simulation in Figure 10 is 36?1 TWh, whereas the alternative
‘maximum generation window’ operation yielded
29?4 TWh,
18,22
the former representing about 10% of UK annual
demand. The more ambitious outer Severn option
4,9
would be
required, together with other small estuary schemes and the use
of pumping, to lift output towards a 15% of UK electricity
demand target, on the basis of these levels of installed capacity
(16DoEn) and ebb mode power generation. Furthermore, the
practicability of rapid introduction of such large power inputs to
the grid will need careful attention. Although this has recently
been broached by the proponents of the Severn barrage,
14
a
switch to dual-mode (two-way) operation and higher installed
capacities (2–36DoEn), leading to shorter and sharper power
pulses from the larger estuary schemes, may create insur-
mountable difficulties to the existing grid function.
It is clear from Figure 10 that a phased introduction of the
schemes in pairs could enable an incremental increase in
capacity while preserving a reasonable power balance across the
generation window, namely by pairing the Severn and Solway,
Morecambe Bay and Wash, and Humber with Mersey/Dee.
Although it is appreciated that the economics are likely to play a
major part in any progression of these major tidal power
proposals, it is reassuring to note that the unit cost estimates
made in the 1980s varied by little more than a factor of 2, with
the Severn and Mersey lowest and the Thames highest.
4,9
5. CONCLUSIONS
This study places on a firm footing the potential of the north-
west to achieve substantial contributions towards renewable
energy targets by exploiting its considerable tidal resources.
With barrage schemes configured with turbine capacity aimed at
minimum unit cost of power produced (equivalent to the 1980s
DoEn studies), in the region of 5% of UK electricity demand, and
about half of regional demand could be secured from barrages
on the Dee, Mersey, Morecambe Bay and the Solway Firth
operating in ebb generation mode. This claim is supported by
the Dee scheme outcomes presented here within the broader
Joule Centre study findings.
18
The power generation would be fully complementary to that
which might be delivered from the Severn barrage. By adding
schemes from the east coast (Thames, Wash, Humber) and a
Severn stage 2 (Bridgewater Bay) scheme, and possibly
increasing the number of turbines together with their use for
temporary ‘pumped storage’, about 15% of present UK electricity
demand should be capable of being met. Unfortunately,
significant continuous generation over a full 24 h window
cannot be demonstrated at this point and follow-up studies of
other potential sites and optimised conjunctive operation studies
are called for. Notwithstanding this, combining such tidal
barrage schemes with the opportunities for tidal stream
installations around the UK coastline, the potential to achieve a
tidal renewable energy contribution to about 20% of present UK
demand would still appear to be realistic.
ACKNOWLEDGEMENTS
The work reported herein has been undertaken as part of project
JIRP 106/03 funded over the period 2006–2008 by the North-
West Regional Development Agency through the Joule Centre.
The views expressed are, however, those of the authors and do
not necessarily reflect those of the sponsors or the host
institutions in which the work was conducted. The final
outcomes of the study are being made available at www.liv.ac.
uk/engdept/tidalpower.
Part of the material presented here formed evidence submitted in
summer 2007 to a governmental review on renewable energy
technologies,
22
although some of the percentage figures quoted
have been revised in the light of more recent electricity
consumption statistics.
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164 Maritime Engineering 162 Issue MA4 Tidal energy potential in UK waters Burrows et al.
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Reviews the physics of tidal power, considering the gravitational effects of the Moon and Sun; semidiurnal, diurnal, and mixed tides; and major periodic components that affect the tidal range. Shelving, funneling, reflection, and resonance phenomena that have a significant effect on tidal range are also discussed. Basic parameters that govern the design of tidal power schemes in terms of mean tidal range and surface area of the enclosed basin are identified. Because energy extracted is proportional to the square root of the tidal amplitude, sites with large tidal amplitudes are best suited for tidal power developments, whereas sites with low tidal amplitudes have sluicing that may be prohibitive. Potential tidal energy developments are mentioned. Existing tidal energy plants are discussed. Tidal barrage design and construction using caissons is examined, as are alternative operating modes, development trends and possibilities, generation cost at the barrage boundary, sensitivity to discount rates, general economics, and markets. Environmental effects, and institutional constraints to the development of tidal barrage schemes are also discussed
A Pragmatic Energy Policy for the UK. Fells Associates
  • Fells Associates
FELLS ASSOCIATES. A Pragmatic Energy Policy for the UK. Fells Associates, Newcastle Upon Tyne 2008. See http://www. fellsassociates.com/. Accessed 22/10/2009.
Severn Tidal Power Phase One Consultation
  • Department Of Energy And Climate
  • Change
DEPARTMENT OF ENERGY AND CLIMATE CHANGE. Severn Tidal Power Phase One Consultation. DECC, London, 2009. See http://www.decc.gov.uk/en/content/cms/consultations/ stp_phase1/stp_phase1.aspx. Accessed 22/10/2009.
Tidal Power from the River Mersey: A Feasibility Study Stage III
  • Mersey Barrage
MERSEY BARRAGE COMPANY. Tidal Power from the River Mersey: A Feasibility Study Stage III. MBC, Liverpool, 1992, p. 401.